Step 3 CCS: Acute Abdomen
Acute abdomen CCS cases test your ability to differentiate surgical from medical emergencies under time pressure. You must rapidly resuscitate, obtain appropriate imaging, and decide whether to consult surgery urgently or manage medically. Appendicitis, bowel obstruction, perforated viscus, and mesenteric ischemia all present differently but share the same initial stabilization approach.
Clinical Approach — What Attendings Do First
The First Minute
- NPO — assume the patient may need surgery
- Two large-bore IVs, normal saline bolus if tachycardic or hypotensive
- CBC, BMP, lactate, lipase, hepatic function panel, urinalysis, urine pregnancy test in women of reproductive age
- Assess for peritoneal signs (guarding, rigidity, rebound) — if present, call surgery NOW
- Pain management: morphine 4 mg IV or ketorolac 30 mg IV (treat pain, do not withhold — it does not mask peritonitis)
Key Orders
- CT abdomen and pelvis with IV contrast (the single most informative test for undifferentiated acute abdomen)
- Upright chest X-ray if perforation suspected (free air under diaphragm)
- RUQ ultrasound if RUQ pain suspected biliary (gallstones, cholecystitis)
- Type and crossmatch if hemodynamically unstable or surgical intervention anticipated
- Lactate level — elevation with abdominal pain raises concern for mesenteric ischemia or strangulated bowel
- Surgical consult early — do not wait for all imaging if clinical picture is concerning
- Broad-spectrum antibiotics if perforation, abscess, or surgical abdomen: piperacillin-tazobactam 4.5g IV or meropenem 1g IV
Time-Sensitive Actions
- Peritoneal signs + hemodynamic instability = emergent surgical consult and resuscitation simultaneously
- Mesenteric ischemia has a narrow window — CTA of abdomen and surgery consult without delay
- Perforated viscus with free air: antibiotics + surgery, do not wait for clinical improvement
- Bowel obstruction with strangulation signs (fever, tachycardia, elevated lactate): surgery, not conservative management
Common CCS Pitfalls
- Withholding pain medication 'to not mask the exam' — this is outdated practice and costs CCS points
- Ordering abdominal X-ray instead of CT for undifferentiated pain — X-ray has poor sensitivity for most pathology
- Not ordering lactate — elevated lactate with abdominal pain is a surgical red flag
- Delaying surgical consult until imaging is complete when peritonitis is obvious clinically
- Forgetting urine pregnancy test in women of reproductive age — ectopic pregnancy must be excluded
Frequently Asked Questions
What imaging should I order for an acute abdomen on CCS?
CT abdomen and pelvis with IV contrast is the workhorse — order it for most acute abdominal pain presentations. If you suspect perforation: start with upright chest X-ray (free air under diaphragm) and/or CT. For suspected biliary disease: right upper quadrant ultrasound first, then HIDA scan if ultrasound is equivocal. For suspected appendicitis in pregnancy or pediatrics: ultrasound first. Never delay surgical consult waiting for imaging if peritonitis is present.
When should I consult surgery immediately in a CCS acute abdomen case?
Call surgery urgently for: peritoneal signs (guarding, rigidity, rebound tenderness), free air on imaging (perforated viscus), signs of bowel strangulation (fever, leukocytosis, lactate elevation with obstruction), mesenteric ischemia (pain out of proportion to exam, lactic acidosis, bloody diarrhea), or hemodynamic instability with abdominal pathology. On CCS, ordering the surgical consult early scores points even before imaging confirms the diagnosis.
How do I differentiate the common causes of acute abdomen on CCS?
RLQ pain + migration from periumbilical + anorexia = appendicitis. RUQ pain + fever + Murphy sign = acute cholecystitis. LLQ pain + fever + leukocytosis in elderly = diverticulitis. Diffuse pain + rigidity + free air = perforated viscus. Colicky pain + distension + obstipation + air-fluid levels = bowel obstruction. Severe pain out of proportion to exam + metabolic acidosis = mesenteric ischemia (surgical emergency).
Related Organ System Topics
Gastroenterology is heavily tested on USMLE Step 3, covering GI bleeding, inflammatory bowel disease, liver disease, pancreatitis, and colorectal cancer screening.
Surgery on USMLE Step 3 covers perioperative management, acute abdominal emergencies, trauma, wound care, and surgical complications.
Emergency medicine on USMLE Step 3 covers the initial evaluation and stabilization of critically ill and injured patients.
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